The present invention relates to a technique that is effective for application to high-frequency power amplifier circuitry which is used to amplify and output high-frequency transmission signals in radio communication system such as mobile phones and an electronic component into which the amplifier circuitry is integrated. More particularly, the invention relates to a technique that is effective for use in high-frequency power amplifier circuitry which is used in mobile phones capable of communication in different modes and different frequency bands, adaptive to a plurality of communication schemes, and an electronic component (power module) into which the amplifier circuitry is integrated.
One of cellular telephone systems, conventionally used for radio communication equipment (mobile communication equipment) such as mobile phones, is a system called Global System for Mobile Communication (GSM) which is used in Europe. This GSM system uses a phase modulation method that is called Gaussian Minimum Shift Keying (GMSK) in which carrier phase shifts encode information to be communicated.
In general, high-frequency power amplifier circuitry is built into the transmitter output section of radio communications equipment. Conventional GSM-compliant radio communications equipment has an arrangement in which the bias voltages to be applied to the high-frequency power amplifier circuitry are controlled to provide an output power required for voice transmission by a control voltage that is output from an “Automatic Power Control (APC)” circuit which generates a transmitting output control signal, based on a signal from a detector to detect a transmitting output and a transmission power level required from a baseband LSI (Patent Document 1). In this arrangement, the amplitude of a signal input to the high-frequency power amplifier circuitry is kept constant.
Meanwhile, a new scheme, Enhanced Data Rates for GSM Evolution (EDGE), has been proposed for use in recent mobile phones. In this scheme, a mobile phone has dual mode communication functions, that is, voice signals are modulated by GMSK when voice communication is performed and data signals are modulated by 8-PSK (Phase Shift Keying) when data communication is performed. The 8-PSK modulates carriers in such a manner that an amplitude shift is added to a phase shift of the carriers modulated by GMSK. The GMSK modulated carrier transmits one bit of information per symbol, whereas the 8-PSK modulated carrier is able to transmit three bits of information per symbol. This, the EDGE scheme enables communication at a higher transmission rate than the GSM scheme.
In communication systems based on the GSM scheme, it is simply required to amplify and output phase-shifted signals according to a required output power level and, therefore, the high-frequency power amplifier circuitry is allowed to operate even in a saturated region of voltage. However, in radio communication systems that enable data transmission and reception according to the EDGE scheme, it is necessary to perform amplitude control and, therefore, the high-frequency power amplifier circuitry is required to perform linear operation in a non-saturated region of voltage.
A method for driving the high-frequency power amplifier circuitry in communication system that can accommodate both the GSM and EDGE schemes has been proposed (Patent Document 2). According to this method, in a GSM mode when GMSK modulation is performed, the amplitude of an input signal to the amplifier circuitry is fixed and bias circuits control the gate bias voltages to be applied to output power FETs. In an EDGE mode when 8-PSK modulation is performed, the gate bias voltages to be applied to the output power FETs are fixed and the output power is controlled by changing the amplitude of the input signal.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2000-151310
[Patent Document 2]
Japanese Unexamined Patent Publication No. 2002-94331